1. Field of the Invention
The present invention relates generally to sensing systems and more particularly to an extended durability sensing system employing one or more sequentially operated sensors.
2. Description of the Related Art
Sensing systems that employ one or more redundant sensors are well known in the art. The motivating factors for employing multiple sensors in these systems are typically to achieve fault tolerance through redundancy, improved measurement accuracy and the ability to cover a wider range of measurements in a finite period of time or space.
It is common to employ sensing systems in extreme temperature and/or corrosive environments, such as the exhaust-gas stream of an internal combustion engine, to monitor critical properties of the environment. The sensors in these systems, which are directly subjected to the monitored environment, may become damaged or otherwise wear-out over time resulting in, inter alia, a degradation in the performance of the sensors. Various approaches have been proposed to combat the premature performance degradation of these sensors. One such approach is to employ multiple redundant sensors that simultaneously monitor an environment. A limitation of this approach is that the performance of all the sensors usually degrades at approximately the same rate, which generally does not extend the durability of the sensing system. Another approach is to substitute conventional sensors with their high performance equivalent. A limitation of this approach is that these sensors typically cost substantially more than conventional sensors rendering them, in some installations, cost prohibitive to use.